Involuntary weight loss can be categorized into three primary etiologies that include, cachexia, sarcopenia and starvation. Cachexia is a debilitating metabolic syndrome associated with numerous diseases, including cancer, AIDS, chronic heart failure (also known as congestive heart failure), chronic obstructive pulmonary disease (COPD), chronic kidney disease, tuberculosis, sepsis and other forms of systemic inflammation. Cachexia varies in its manifestations, but generally involves involuntary loss of skeletal muscle mass and some form of underlying illness (Evans et al. (2008) CLIN. NUTR. 27:793-799). Cachexia is a wasting disorder involving involuntary weight loss and may be associated with systemic inflammation and/or an acute inflammatory response. Thomas (2007) CLIN. NUTRITION 26:389-399. Loss of fat mass as well as fat-free mass, such as muscle mass, often is a prominent clinical feature of cachexia. In many but not all cases, cachexia progresses through stages that have been designated precachexia, cachexia and refractory cachexia (Fearon et al. (2011) LANCET ONC. 12:489-495). Two different, but sometimes overlapping, processes appear to drive the development and progression of cachexia: (a) metabolic processes that act directly on muscle, reducing its mass and function; and (b) reduced food intake, which leads to loss of both fat and Muscle (Tsai et al. (2012) J. CACHEXIA SARCOPENIA MUSCLE 3:239-243).
Although cachexia is a complex and incompletely understood syndrome, it is clear that GDF15 (also known as MIC-1, PLAB, PDF and NAG-1), a member of the TGF-β superfamily, is an important mediator of cachexia in various diseases (Tsai et al., supra). At least some tumors over-express and secrete GDF15, and elevated serum GDF15 levels have been associated with various cancers (Johnen et al. (2007) NAT. MED. 13:1333-1340; Bauskin et al. (2006) CANCER RES. 66:4983-4986). Monoclonal antibodies against GDF15 have been recognized as potential anti-cachexia therapeutic agents. See, e.g., U.S. Pat. No. 8,192,735.
Weight loss resulting from cachexia is associated with poor prognosis in various diseases (Evans et al., supra), and cachexia and its consequences are considered to be the direct cause of death in about 20% of cancer deaths (Tisdale (2002) NAT. REV. CANCER 2:862-871). Cachexia is infrequently reversed by nutritional intervention, and currently this syndrome is seldom treated with drug therapy (Evans et al., supra).
Sarcopenia is a clinical condition related to cachexia that is characterized by loss of skeletal muscle mass and muscle strength. The decrease in muscle mass can lead to functional impairment, with loss of strength, increased likelihood of falls, and loss of autonomy. Respiratory function may also be impaired with a reduced vital capacity. During metabolic stress, muscle protein is rapidly mobilized in order to provide the immune system, liver and gut with amino acids, particularly glutamine. Sarcopenia often is a disease of the elderly; however, its development may also be associated with muscle disuse and malnutrition, and may coincide with cachexia. Sarcopenia can be diagnosed based upon functional observations such as low muscle weight and low gait speed. See, e.g., Muscaritoli et al. (2010) CLIN. NUTRITION 29:154-159.
Starvation typically results in a loss of body fat and non-fat mass due to inadequate diet and/or nutritional uptake (Thomas (2007) supra). The effects of starvation often are reversed by improving diet and nutritional, for example, protein, uptake.
Naturally occurring antibodies are multimeric proteins that contain four polypeptide chains (FIG. 1). Two of the polypeptide chains are called heavy chains (H chains), and two of the polypeptide chains are called light chains (L chains). The immunoglobulin heavy and light chains are connected by an interchain disulfide bond. The immunoglobulin heavy chains are connected by interchain disulfide bonds. A light chain consists of one variable region (VL in FIG. 1) and one constant region (CL in FIG. 1). The heavy chain consists of one variable region (VH in FIG. 1) and at least three constant regions (CH1, CH2 and CH3 in FIG. 1). The variable regions determine the specificity of the antibody. Each variable region comprises three hypervariable regions also known as complementarity determining regions (CDRs) flanked by four relatively conserved framework regions (FRs). The three CDRs, referred to as CDR1, CDR2, and CDR3, contribute to the antibody binding specificity. Naturally occurring antibodies have been used as starting material for engineered antibodies, such as chimeric antibodies and humanized antibodies.
There is a significant unmet need for effective therapeutic agents for treating cachexia and sarcopenia, including monoclonal antibodies targeting GDF15. Such therapeutic agents have the potential to play an important role in the treatment of various cancers and other life-threatening diseases.